[PATCH] D151834: Include math-errno with fast-math

Aaron Ballman via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Tue Sep 12 08:51:06 PDT 2023


aaron.ballman added a comment.

In D151834#4644375 <https://reviews.llvm.org/D151834#4644375>, @zahiraam wrote:

> In D151834#4644373 <https://reviews.llvm.org/D151834#4644373>, @aaron.ballman wrote:
>
>> In D151834#4643925 <https://reviews.llvm.org/D151834#4643925>, @uabelho wrote:
>>
>>> Hi @zahiraam ,
>>>
>>> I have a couple of downstream testcases that fail with this patch.
>>> Before
>>>
>>>   > clang bbi-86364.c -lm -O3
>>>   > ./a.out
>>>
>>> passed but with the patch the assert in the program fails:
>>>
>>>   a.out: bbi-86364.c:9: int main(): Assertion `(*__errno_location ()) == 33' failed.
>>>
>>> Is this as expected?
>>>
>>> F29200339: bbi-86364.c <https://reviews.llvm.org/F29200339>
>>
>> This seems unexpected to me and it seems to relate to whether you include errno.h or not: https://godbolt.org/z/EPWzazx9r -- @zahiraam do you have ideas as to what's going on?
>
> I haven't looked at it as I saw that the comment has been deleted. Let me look into it.

Oh, it's not the inclusion of errno.h that matters, it's the declaration of `__errno_location`: https://godbolt.org/z/zo4PaPEME -- it seems that inclusion of `__attribute__ ((__const__))` is what makes the distinction: https://godbolt.org/z/1bePhvaG4


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